Anti-static material and method of application



June 27, 1961 L. J. NOVAK 2,

ANTI-STATIC MATERIAL AND METHOD OF APPLICATION Filed Sept. 30, 1959 .SAR (specific air resist/my) Res/n App/fed on Uniz Weigh! of Fabric Fig.

Fiber Res/stance COTTON WOOL SILK

' ACETATE OALON TERYLENE Pe/afive Values of Res/lszance of Clean Fiber 02 70% 19.15.

INVENTOR Fig. 2 4:0 wvovAK ATTORNEYS UQi C States Pmfl O" 2,990,299 ANTI-STATIC MATERIAL AND METHOD OF APPLICATION Leo J. Novak, Dayton, Ohio, assignor to The Commonwealth Engineering Company of Ohio, Dayton, Ohio Filed Sept. 30, 1959, Ser. No. 843,549 18 Claims. (Cl. 117-1395) x invention relates to antistatic compositions and methods for treating textiles to render the same antistatic. The invention is more particularly concerned with the discovery of new antistatic materials which are useful for treating fibers and fabrics to render the same tn'bo-electrically conductive. The invention overcomes the difficulties encountered with electrostatic charges on various fibers and filaments during the manufacture and treatment.

The principal object of the invention is to provide an antistatic material and method for treating fibrous materials, especially textiles, garments and the like, to render the" same tribo-electrically conductive, and which retain this property for long periods of time. In accordance with the present invention there is provided tribo-electrochemically conductive substances which are deposited on the fibers to produce textile fibers which are resistant to building up of static electricity.

Static electrical charges cause a host of difficulties in the manufacture and uses of fibers and filaments. Some of the ditficulties encountered because of static electrical charges on fibers and fabrics are:

(1-) Repulsion of similarly charged materials causing bowing out and doubling up of filaments of adjacent, contiguous yarns during manufacture of fabrics;

' (2) The weft ends of fibers are hard to tuck in place on the loom, and it is difliicult to fold the cloth neatly as it comes from the driving machine;

(3) Soiling of the fiber by the attraction of foreign particles which carry in opposite charge or no charge clinging to the fiber;

(4) Sticking and clinging of folded fabric and cloth portions is encountered and which is a contributing factor in the failure of parachutes to open properly;

(5) Electric sparks are produced which result in explosions, and fires under certain conditions, as well as causing interference with the proper operation of radio, radar and electronic equipment;

(6) Electrical shocks caused by sudden grounding of static electric charges are discomforting to persons sustaining the same;

(7) Static electricity causes clothing to cling which is-unpleasant to the wearer of such clothing.

It is known that the newer synthetic fibers, such as made from polyethylene, ethylene glycolteraphthalic acid polymers (Dacron), etc., have less conductance than the hydrophilic cellulosic fibers, for example cotton, rayon, etc.

In the preparation and processing of hydrophobic fibers, however, the manufacturer is troubled to a greater improvement. Such treatment gives the fiber twenty times the moisture regaining power than analogous cellulosic fibers which regain about 22% moisture at 60% relative humidity.

Static frictional electrical charges which build up during fiber production and handling is becoming an acute problem because of the development of new hydrophobic fibers and the increased production speeds used in their preparation. At the British Textile Institute Overseas Conference at Zurich in 1956, the main topic and problem discussed was Textile Static Electricity.

In this connection, Table I shows the relationship between fiber surface resistivities and RH. (relative humidities). With increase in surface resistivities, the fiber surface static electricity formation is increased as shown in Table I.

. TABLE I [Surface resistivities of fabrics in ohms/square inch] Cotton, Wool, Nylon, Temp., 0. R.H. 6 oz. 16 oz. 4 oz.

Oxford Serge Oxford 50 2x10 axio 2x10 Q 1x10 3x10 9x10 4 3x10 5x10 5x10 4 72x10" 72 10 72x10" While the ideal antistatic agent for fibers should be hygroscopic and have a high ion concentration as well as resistance to washing and cleaning, the hygroscopic requirements are difiicult to obtain along with the washing resistance requirements since most hygroscopic materials are water-soluble.

A possible solution to the problem, however, appears possible through controlled polymerization of polyelectro-" lyte type polymers on the fiber to give insoluble surface polymer coatings which absorb water, retain it, and which are insoluble in water, but furnish some ionizable groups Both anionic and cationic polyelectrolyte groups could be used, for example, carboxylic, sulfonic, phosphoric, and amine or sulfonium, respectively. Cross linking of ethylenic (vinyl) or epoxy groups with condensation reactions yields ester, ether, ammonium and/or urethane groups which produce a compound having antistatic characteristics.

-High humidities have been found to decrease static electricity, however, synthetic fibers do not pick up any significant amounts of moisture and thus readily accumulate electrical charges. The following table presents data which shows the relative humidity (R.H.) needed to lower the electrical charges:

TABLE II R.H. needed to reduce resistance of clean fibers to 10 ohmslgrm/cmfi] Patented June 27, 1961 i r 3 a In the above table,'it will be observed that, in general, the synthetic organic fibers require a much higher relative humidity (R.H.) than natural fibers to effectively overcome the tendency to accumulate electrical charges.

The following types of antistatic materials are listed together with their usefulness as antistatic substances.

TABLE HI Substance Type Remarks as to Utility Value Oils, parafiiuic.; Lubricant i Temporarily effective. Quaternary Ionizing, moisture Good but solubility ammonium salts. retention. shortens life. Radioactivesalts Alphaflimd Beta Ray Good but expensive. emi ers. Glycol fatty acid Lubricant Fair but solubility esters. shortens life. Fattydacid amines, Ionizing lubricant..-" Temporarily efiective.

am es. 7 I Polymers Moisture retention, Good but expensive conduction. to apply and changes fiber v characteristics. Polyhydroxy esters Moisture retention Temporarily effective,

' lubricant.

The new antistatic substanceswithin the purview of this invention are:

(1) Aromatic or heterocyclic carbohydrate polymers and ethers. An example 'of this class being benzylated and naphtholated dextran.

, (2) Carboxyalkyl carbohydrate polymers and ethers, such as the mixed aromatic carboxyalkyl ethers of carbohydrate polymers. An example of such a compound being carboxymethyl benzyl dextran.

, (3) Salts of mixed aromatic carboxyalkyl ethers of carbohydrate polymers, for example the sodium salt carboxymethyl' ether of dextran.

These metal salts of mixed aromatic carboxyalkyl ethers of carbohydrate polymers, particularly 'carboxymethyl benzyl dextran (CMBD) having a D8. (degree of substitution) of methyl groups equal to between 0.3 and 0.5, and a high benzyl D8. of 1.3 to 2.0 have been discovered to be excellent antistatic substances. The salts of aluminum, ammonium and calcium are especially useful for conducting electrical charges from fibers, filaments and the like.

v In the draWing-- FIGURE 1 shows a graph in which the electrical conductance of a fiber is expressed in terms of specific area resistivity (SAR). The. curve on thegraph of FIGURE 1 shows the results obtained using polyethylene glycol dichloride with hexamethylenediamine onnylon fabric. As will be observed, when approximately 1% 'by weight of the fabric comprises antistatic the specific area resistivity is lowest and remains substantially constant with this amount present. 7

resistance of synthetic fibers to conductance of electrical charges at 70% relative humidity'as compared with natural fibers suchascotton. Terylene synthetics, e.g., polyethylene terephthalate fibers being the most resistant to the conductance of tribe-electricity.

The improved antistatic compounds found to have enhanced antistatic properties ,are the acidic carboxyalkyl alkylated compounds and their salts, or mixed aromatic carboxyalkyl ethers of carbohydrate polymers.

In accordance with the invention, a carbohydrate polymer such as dextran, starch, amylose, amylopectin, cellulose, or the like, is carboxyalkylated to form a derivative containing active carboxyl (acidic) groups. The degree of substitution (D.S.) of the carboxyalkyl (CA) radical into the carbohydrate polymer is held to a low D .S.

FIGURE 2 of the drawing shows the relativelyhighi and within a range of 0.01 to 0.5. The carboxyalkyl (CA) derivative is then treated with a halide ofaparticular organic compound in the presence of alkali (OH- ions) to introduce the organic radical into the CA-carbohydrate polymer. The following organic groups and analogous halides are representative- TABLE IV Organic radical: Halide Benzyl Benzyl chloride Benzoyl Benzoyl chloride Naphthyl Naphthoyl chloride Palmitic l Palmitoyl chloride Stearic Stearyl chloride Ammonic Ammonioyl chloride The carboxylic derivative is formed by the Schotten- Baumann method, that is the hydroxy compound to be reacted, e.g., benzylated, is shaken with benzylchloride in aqueous alkali solution to form the mixed ether or ether-ester derivative of the carbohydrate. I

An example'of the carbohydrate derivative found to have antistatic properties is carboxymethyl benzyl dextran, and such as made from native hydrolyzed dextrans,

and'the metal salts thereof. These compounds are ionizable because of the presence of carboxyl radicals, as shown:

The compounds, however, are notvery soluble in neutral or acidic aqueous solutions, and are only slightly soluble in highly alkaline aqueous media at pH values higher than those commonly encountered in aqueous washing solutions used for cleansing clothes, etc. The metal salts of these compounds have been found particularly suitable as tribe-electrically conductive agents, and such ascommonlyreferred to as antistatic agents. Calcium carboxymethyl benzyl dextran, for example, is practically insoluble in aqueous solutions at pH values between 2.0 and 11.0. On the other handwhen the compound is deposited onfibers or filaments, in accordance with the present invention, the compound changes the electrical conductivity of the fiber so that fibers conduct away triboelectricity even in the dry fiber state. Carboxymethyl benzyl dextran is also effective but to a lesser degree than the salts.

The following examples are illustrative of the invention:

Example 1 'Carboxymethyl benzyl dextran prepared from native NRRL B-512v dextran having a low carboxymethyl 'D.S. (D'.S.=='0.l to 0.3) and a high degree of substitution or benzyl radical (D.S.=l.0 to 2.0) is dissolved in a mixture by weight of-% dioxolane and 20% water.

The resultant solution containing 10% CMBD was sprayed onto viscose rayon fibers until the surfacewas fully wetted, after which the thus wetted fibers were air dried over night. A 5% increase in fiber weight was obtained and the coated fibers showed an electrical resistance of only 1 0% of the untreated fibers. Thetreated fibers at 27% relative humidity had a resistance 01510 ohms/gm./c'in.

After washingthe treated fibers in a 2% solution of sodium lauryl sulfate at 70 C. for fifteen minutes and airdrying for 24 hours, the fibers still retained substantially the same electrical resistance-as before the washing treatment.

and removed and excess liquid drained off. The fabric was then dipped in a 10% aqueous solution of CMBD I (Example l) in 80% dioxolane'and 10% water. After five minutes immersion, the fabric was removed, washed twice with water-and dried at 80 C. for 24 hours. The resultant dried nylon fabric was weighed and found to have gained 3/; of 1% in weight.

The fabric, thus treated, showed that the electrical resistance was reduced to substantially of the original untreated fabric, being approximately 2x10 ohms per gm/omfi.

After washing the thus treated fabric in a 2% aqueous soap solution (soap flakes) at 90 C.,for ten minutes and then drying at 80 C. for 24 hours, the change in electrical resistance was not significant.

Example 3 Dry cleaning solution as in Example 1 containing the aluminum salt of CMBD and when applied to polyethylene glycol terephthalate (Dacron) fabric has the fabric antistatic properties and which was markedly superior to such fabric treated with cleaning solvent containing sodium salt of glycerol monolaurate as a detergent.

Example 4 A solution consisting of 5% by weight of the ammonium salt of CMBD is used to treat cellulose acetate fabric whereby 0.5% by weight of the fabric comprises said ammonium salt. This provides a fabric exhibiting excellent antistatic properties.

Example 5 In this instance the calcium salt of CMBD is used as in Example 1 to provide a fabric made of synthetic filaments which possess good antistatic properties.

In the antistatic compositions of the invention which comprise carboxymethyl benzyl dextran (CMBD) as set out in the examples, comprising organic solvents which are miscible with water. The solution, however, when further diluted with water causes the CMBD to precipitate as the organic salt. Further, it has been observed that the presence of alkali salts for example sodium chloride or sodium stearate in solution, tends to bring about precipitation of the CMBD or its salts, e.g., sodium, calcium, aluminum or magnesium salts of CMBD. This property is of great advantage because upon precipitation of the CMBD onto the fibers the same is insoluble in the alkali soap waters such as commonly used for washing and cleaning of the fibers or fabrics. The CMBD salts are also insoluble in the conventional dry cleaning solvents for example Stoddards solvent, naphtha, carbon tetrachloride and perchlorethylene.

In accordance with the invention, the fabric or fibers to be rendered triboelectrically conductive are treated with a solution of the antistatic salt and in sufiicient concentration whereby, upon evaporation of the solvent, the fabric comprises from 0.1% to 1.5% by weight of the antistatic agent based on the dry fabric thus treated.

After the clothes or fabric have been washed clean, the clothes are preferably transferred to a drier, for example a gas or electrically heated drying tumbler where the clothes are air dried at 250 to 300 F. The cleaning solution in each instance contains sufiicient amount of the antistatic substance whereby after drying there is left on the clothes from 0.1% to 1.5% by weight of the clothes of antistatic material.

If desired, the clothes may be cleaned with dry cleaning solvent substantially free of the antistatic agent and after the dry cleaning treatment, rinsing the clothes in an organic solvent containing the requisite amount of antistatic heat-stable substance.

Various modifications and changes may be made in the fiber treating procedure and additional substances may be added to the antistatic substances to enhance their effectiveness as desired without departing from the spirit and scope of this invention, and as hereinafter more particularly defined in the appended claims.

What is claimed is:

1. A method of treating fibers, filaments and fabrics to render the same tribe-electrically conductive comprising treatingsaid fibers with a solution containing a carboxyalkylated derivative of dextran and water.

2. A method of treating fibers, filaments and fabrics to.

3. A- method of treating fibers, filaments and fabrics to render the same tribe-electrically conductive comprising treating said fibers with a solution containing acarboxymethyl benzyl dextran and water.

4. A method of treating fibers, filaments and fabrics to render the same tribo-electrically conductive comprising treating said fibers with an aqueous solution containing a carboxyalkylated derivative of a dextran wherein the D.S. of the carboxyalkyl is between 0.01 and 0.5.

5. A method of treating fibers, filaments and fabrics to render the same tribe-electrically conductive comprising treating said fibers with an aqueous solution containing a carboxymethyl benzyl dextran and wherein the dextran is native NRRL B-512 dextran having a low carboxymethyl D.S. of 0.1 to 0.3, and a high D.S. of benzyl radical of 1.0 to 2.0.

6. A method of treating fibers, filaments and fabrics to render the same tribe-electrically conductive comprising treating said fibers with an aqueous solution containing a salt of a carboxyalkyl derivative of dextran.

7. A method of treating fibers, filaments and fabrics to render the same tribe-electrically conductive comprising treating said fibers with an aqueous solution containing a salt of a car-boxyalkyl derivative of dextran, said salt being selected from the group consisting of sodium, aluminum, ammonium and calcium and mixtures thereof.

8. A method of treating clothes to render the same antistatic which comprises applying to said clothes a solvent solution containing an antistatic substance comprising a salt of carboxymethyl benzyl dextran, said salt containing 0.3 to 0.5 D.S. of carboxymethyl and a D.S. of benzyl of 1.3 to 2.0.

9. A method of treating clothes to render the same antistatic which comprises applying to said clothes a solvent solution containing an antistatic substance comprising a salt of carboxymethyl benzyl dextran, said salt being a salt of the group consisting of sodium, aluminum, ammonium, and calcium, and mixtures thereof, said salt containing 0.3 to 0.5 D.S. of carboxymethyl and a D.S. of benzyl of 1.3 to 2.0.

10. A method of treating clothes to render the same antistatic which comprises applying to said clothes a solvent solution containing an antistatic substance comprising a salt of carboxymethyl benzyl dextran, said salt containing 0.3 to 0.5 D.S. of carboxymethyl and a D.S. of benzyl of 1.3 to 2.0, said antistatic substance being dissolved in a solvent mixture of dioxoline and water wherein water constitutes no more than about 20% by Weight of said solvent mixture.

11. A tribe-electrically conductive composition adapted to be applied to fibers to coat and impregnate the same consisting of a salt of carboxyl ated derivative of dextran.

12. A tribo-electrically conductive composition adapted to be applied to fibers to coat and impregnate the same consisting of a salt of carboxyalkyl derivative of dextran.

13. A tribe-electrically conductive composition adapted to be applied to fibers to coat and impregnate the same consisting of a dextran derivative selected from the group consisting of an ether, mixed ether and ether-ester.

14. A tribe-electrically conductive composition adapted to be applied to fibers to coat and impregnate the same consisting of a salt of carboxymethyl benzyl dextran.

15. A tribo-electrically conductive composition adapted to be applied to fibers .to coat and impregnate the same consisting of an aqueous solution containing a calcium carboxymethyl benzyl dextran.

16. A tribe-electrically conductive composition adapted to be 'applied to fibers to coat andimpregnate the same consisting of all-aqueous solution of sodium carboxymethyl benzyl dextran. t t

17. A tribo-electri-callyconductive composition adapted to be applied to fibers to coat and impregnate'the same consisting of an aqueous sol-ution of aluminum qarboxy-methyl benzyldextran. V f

18. A tribe-electrically conductive composition adapt ed to be applied to fibers to coat and impregnate the same consisting of an aqueous solution ofmagnesi-um;

carboxymethyl benzyl dextran.

References Cited in the file of this patent,

, UNITED STATES PATENTS 

1. A METHOD OF TREATING FIBERS, FILAMENTS AND FABRICS TO RENDER THE SAME TRIBO-ELECTRICALLY CONDUCTIVE COMPRISING TREATING SAID FIBERS WITH A SOLUTION CONTAINING A CARBOXYALKYLATED DERIVATIVE OF DEXTRAN AND WATER. 